Buffalo Chicken macaroni and Cheese

4 T. unsalted butter
kosher salt
1 lb. macaroni
1 small onion, finely chopped
2 stalks celery, finely chopped
3 C. shredded rotisserie chicken
4 cloves garlic, minced
3/4 C. buffalo hot sauce, divided
2-1/2 C half-n-half
2 T. all-purpose flour
2 t. dry mustard
1 lb. yellow sharp cheddar cheese, cut into cubes
8 oz. pepper jack cheese, cut into cubes
2/3 C. sour cream
1 C. panko breadcrumbs

1. Preheat the oven to 350 and spray a 9x13 baking dish with butter cooking spray.  Bring a large pot of salted water to a boil; add pasta and cook until al dente.  Drain.

2. Meanwhile, melt 2 T. butter in a large skillet over medium heat.  Add the onion and celery and cook until soft, about 5 minutes.  Stir in the chicken and garlic and cook 2 minutes, then add 1/2 C. hot sauce and simmer until slightly thickened, about 1 minute more.

3. Melt 2T. butter in a saucepan over medium heat.  Stir in the flour and mustard with a wooden spoon until smooth.  Whisk in the half-and-half, then add the remaining 1/4 C. hot sauce and stir until thick, about 2 minutes.  Whisk in the cheddar and pepper jack cheeses, then whisk in the sour cream until smooth.

4. Combine chicken mixture, cooked macaroni and cheese sauce and pour into the prepared baking dish.  Sprinkle with panko breadcrumbs and bake until bubbly, about 30-40 minutes.  Let rest 10 minutes before serving.